Sentic

iTrader: (1)

Then you probably have too much spring for the damper. You don't loose it, it is always better to be able to adjust, just gotta match it up. And of course, everybody has different expectations.

A softer spring, with stiffer swaybars and adjustable dampers would be nice for the street imho.

JasonC SBB

This is not correct. Both bump and rebound do everything - spring rate matching, ride comfort, and traction. Weight too.

Having much more low to mid speed rebound than bump is good for cars/trucks/SUVs that have a high CG and soft springs. It lets them pack down onto the bumpstops and temporarily lower CG and raise effective spring rates during transients. It works well too for autox where the rules require stock springs.

In a street miata it is the wrong approach.

The correct values and slopes and shapes of the low, mid, high speed rebound and bump damping, has been the subject of simulation and research by FCM. I worked with FCM developing simulation tools. FCM did the time consuming work of valving the curves "good" predicted by the simulations and testing them. He has come up with curves that many customers are very pleased with. Even I am surprised by reviews like this:


So much so that it makes me wonder why other aftermaket cos, and the OEM's don't often do as well despite their big bux R&D.
I suspect part of it is overlawyering.

It's not that simple.

Read my posts in this thread:
Damping Rate Confusion, Shock Dyno graphs included, Kinda Long - MX-5 Miata Forum

JasonC SBB

This dyno plot has too little resolution to show features other than simple low vs hi speed damping.

Braineack

iTrader: (62)

yeah sorry best I can do without raw dataz. I'm just trying to understand it all better in general. But it seems from what little reading I can find what I don't like about my shock is the crazy high initial rebound, just like you suggest.

I'm also trying to figure out how one determines what rate springs would work best just going on the dyno curve? or can you?



Likewise, after reading review after of review of people with rates as low as 300/200 or as high as 700 on the FCM revalve, there is no complaint on ride quality nor performance. Ultimately it seems that's the best way to go about it.

JasonC SBB

You look at the average slope of both bump and rebound, up to 3 ips, by eyeballing the area under the curve.

The correct slope is a function of spring rate and the weight of the car. I don't have the numbers off the top of my head.

If you want to derive it you first work with wheel rates then work your way back using the motion ratio. The correct damping ratio is 0.65 of critical. However a lower damping ratio works if the knee is at a higher velocity, a higher ratio works if the knee is at a lower velocity. Be careful of the factor of 2 - depending how you calculate, it's either multiplied by 2 or divided by 2. You get it wrong, you'll be off by a factor of 4!

Braineack

iTrader: (62)

yeah. i think ill just save my pennies and do it right eventually if I'm still unhappy after swap the springs and tophats. Car probably has 4K miles on it in the last 2 years, so whatever.